1. Field of the Invention
The present invention relates to an improvement of a magnet generator type ignition system, which is used for an engine with comparatively small dimensions.
2. Description of the Prior Art
Conventionally, such an ignition system is known in, for example, Japanese Utility Model Application Laid-open No. 63-21739 and Japanese Patent Application Laid-open No. 542629, in which a permanent magnet is fitted to the outer periphery of a rotor.
The above-mentioned conventional arrangement in which a permanent magnet is fitted to the outer periphery of a rotor has the problems (1) to (3) below. That is to say, (1) in order to maintain the rotational balance of the rotor, it is necessary to fit a counterweight to the rotor on the side opposite to the permanent magnet, the counterweight having a weight that is comparable to the permanent magnet, thereby making the rotor very heavy. Furthermore, (2) it is necessary to arrange the structures of the sections to which the permanent magnet and the counterweight are fitted and the method for fitting them so as to withstand the centrifugal force generated by high rotational speed. Moreover, (3) since there is only a small space inside the sections to which the permanent magnet and the counterweight are fitted, it is difficult to place another component inside the sections to which the permanent magnet and the counterweight are fitted.
The present invention has been conducted under the above-mentioned circumstances, and it is an object of the present invention to provide an engine ignition system that can reduce the weight of the rotor while allowing the rotational balance of the rotor to be easily adjusted, simplify the arrangement of the rotor itself, and secure an effectively usable space in the region on the inside of the rotor in the radial direction.
In accordance with one feature of the invention, there is provided an engine ignition system that includes a rotor that rotates in synchronism with the rotation of an engine. An iron core is fixedly disposed opposite the outer periphery of the rotor, and a primary coil and a secondary coil are wound concentrically around the iron core. A spark plug can be fired in synchronism with the rotation of the rotor. The permanent magnets are fitted to the iron core having a plurality of legs opposite the outer periphery of the rotor, the legs are positioned so they are spaced in the peripheral direction of the rotor, and an inductor is fixed to the outer periphery of the rotor. The inductor forms a magnetic path for the magnetic flux that is formed by the permanent magnets between a pair of the legs that are adjacent to each other in the peripheral direction of the rotor. The winding of the primary coil and the secondary coil around the iron core enable the spark plug to be energized every time the inductor passes the pair of legs.
In accordance with the above-mentioned arrangement, since the rotor is provided with only the inductor for forming the magnetic path for the magnetic flux generated by the permanent magnets on the iron core side, the weight of the rotor can be reduced and the rotational balance of the rotor can be easily adjusted and, moreover, the inductor can be easily provided on the rotor in comparison with the conventional arrangement in which a permanent magnet is fitted to a rotor. Furthermore, a comparatively large space can be secured in the region on the inside of the rotor in the radial direction, and the space can be used effectively.
Furthermore, there is provided an engine ignition system wherein the iron core is provided with three legs that are spaced at equal intervals in the peripheral direction of the rotor, the permanent magnets are fitted to at least each of the legs on opposite sides along the peripheral direction of the rotor, and the primary coil and the secondary coil are wound around the leg that is in the middle along the peripheral direction of the rotor. In accordance with such an arrangement, the rate of change in the magnetic flux due to the inductor passing over the middle leg among the three legs as the rotor rotates is greater than the rate of change in the magnetic flux due to the inductor passing over two legs when only two legs are provided, thereby giving a high ignition energy.
In accordance with another feature of the invention there is provided an engine ignition system wherein the permanent magnet is mounted within a cutout provided in the iron core, and in accordance with such an arrangement, the permanent magnet can be easily fitted and fixed to the iron core.
In accordance with another feature of the invention there is provided an engine ignition system wherein the permanent magnets are fitted to a face of the iron core, the face being opposite the rotor, and in accordance with such an arrangement, leakage of magnetic flux can be suppressed.
In accordance with another feature the invention there is provided an engine ignition system wherein the inductor projects out of the outer periphery of the rotor toward the iron core, and in accordance with such an arrangement, the inductor can be easily formed.
In accordance with another feature of the invention there is provided an engine ignition system wherein the inductor is formed by fitting a magnetic plate to the outer periphery of the rotor, and in accordance with such an arrangement, the inductor can be easily formed while obviating the need for a die, etc.
In accordance with another feature of the invention there is provided an engine ignition system wherein the inductor is formed by embedding a piece of magnetic plate in the rotor that is made of an aluminum alloy by die casting, and in accordance with such an arrangement, the inductor can be easily formed by simply fitting and fixing the magnetic plate to the rotor that is made of an aluminum alloy, which is a non-magnetic material.
In accordance with another feature of the invention there is provided an engine ignition system wherein the inductor is formed by inwardly recessing a part of the outer periphery of the rotor, and in accordance with such an arrangement, the inductor can be easily formed.